Here is the foregrip I put together for a co2 pistol https://youtu.be/7XnKiVm1c6o
The hole is undersized (on purpose) so you might need to drill out the hole using a 1/2" drill bit. The rail mount should fit this piece of rail nicely. https://amzn.to/2S88TtN The rail will need to be epoxied onto the grip.
Print however you like but I recommend some supports and 3 or more perimeters. Also, a slightly higher temp should help with layer adhesion which is important.
The author hasn't provided the model origin yet.